Term graph Definition: A picture, image, or diagram that is used to display information. Graphs are most commonly used in the economics to depict relations between two variables, that is a two-dimensional graph. The market diagram is perhaps the most noted graph used in economics. This graph reflects the market price on the vertical axis and the quantity exchanged on the horizontal axis. The two key relations depicted on the graph are the demand curve, which is an inverse relation between price and quantity, and the supply curve, which is a direct relation between price and quantity.